1. Field of the Invention
The present invention relates to a measuring method, and in particular to a method of measuring pore depth on the surface of a polishing pad during processing.
2. Description of the Related Art
During the manufacture of integrated circuits it is necessary to polish a thin wafer of semiconductor material to remove material and dirt from the surface thereof. Typically, a wet chemical abrasive or slurry is applied to a motor driven polishing pad while a semiconductor wafer is pressed against it in a process well known as chemical mechanical polishing (CMP). The polishing effects on the wafer result from both the chemical and mechanical actions.
The polishing pad contacts the wafer surface while both wafer and pad are rotating on different axes. The rotation facilitates the transport of the abrasive-containing polishing slurry between the pad and the wafer. The condition of the polishing pad directly affects the polishing rate of material removal and uniformity of the removal from the semiconductor wafer. Pad conditioning may take place during or after the polishing process. The most common method of pad conditioning is a mechanical abrasion of the pad surface. Materials such as steel blades or abrasive wheels are often used. While conditioning of the pad surface improves polishing uniformity and rates, it has the detrimental effect of removing a quantity of pad material. However, the polishing removal rate is still diminished, since the pores on the surface of the polishing pad retain particles within the slurry. Therefore, the polishing removal uniformity is degraded.
Presently, the only means available to measure pad condition is destructive to the polishing pad, such as cutting a piece from the pad and using a micrometer to measure surface depth. Thus, pad destruction may result and downtime is increased.
Accordingly, an object of the present invention is to measure pore depth and size on the surface of a polishing pad during processing without pad destruction.
According to the above mentioned objects, the present invention provides a method of measuring pore depth and size on the surface of a polishing pad during processing.
In the method of the present invention, a planar ultrasound sensing device is disposed a predetermined distance above the surface of a polishing pad. The planar ultrasound sensing device sends out a plurality of ultrasound signals to the surface and the pores therein, and receives a plurality of reflected signals from the pad surface and constituent pores. The difference between pore depth and the surface is determined to establish first depth difference data according to the time delay in the reflected signals. The polishing pad is then rotated to obtain second to Nth depth difference data. A relational image relative to the surface and the pores of the polishing pad is obtained according to the first to Nth depth difference data.
Also, the present invention displays the relational image relative to the surface and the pores of the polishing pad.
Also, the present invention computes a relationship between size and depth of the pores on the polishing pad according to the first to Nth depth difference data.
Also, the present invention calculates the pore size per unit surface area of the polishing pad according to the pore size and surface area of the polishing pad.
A detailed description is given in the following embodiments with reference to the accompanying drawings.